The present invention relates to spectacles featuring liquid crystal lenses.
If the focal adjustment function of the eyeballs deteriorates due to presbyopia or the like, the patient has conventionally used two pairs of spectacles with different focal lengths for the affected ranges of vision, as required. In this case, however, the user has had to take the trouble always to carry both types of spectacles for alternative use.
Conventionally, so-called bifocal spectacles have been developed whose lenses include a region of a shorter or longer focal length to be used for shorter or longer distances. In spectacles of this type, however, the eye can only focus on objects in the corrected visual field. Thus, the bifocal glasses cannot provide the large field of vision provided by ordinary glasses.
If the crystalline of a patient's eyeball suffering from cataract is removed, the patient must obtain several pairs of spectacles of different focal lengths and use them accordingly.
To solve these problems, there are provided such liquid crystal spectacles as are disclosed in, for example, Japanese Patent Publication No. 50339/83. These spectacles use variable-focus lenses (hereinafter referred to as liquid crystal lenses) which take advantage of a property of a liquid crystal such that its transmission factor is varied by controlling the applied voltage. The orientation of the liquid crystal molecules is controlled by externally applying an electric or magnetic field to a liquid crystal cell including the molecules oriented in one direction, thereby continuously changing the refractive index of the liquid crystal. The refractive index of this liquid crystal lens is variable, so that its focal length can be set freely.
A problem in the practical use of the liquid crystal spectacles lies in the manipulation of a drive circuit and a power source for applying voltage to the liquid crystal lenses. To cope with this, separate-type liquid crystal spectacles have been proposed. According to these spectacles, the power source and drive circuit are housed in a case independent of the spectacle body frame. In this case, the user must take the trouble to carry the case separately whenever he or she uses the glasses. When pocketing the case, for example, a cord or cords must connect it with the lenses. The cords are troublesome in handling and mar the appearance of the spectacles. Also, they are liable to pick up undesired external noise, exerting a bad influence upon the liquid crystal lenses. In the absence of a suitable pocket, moreover, the user must carry the case in his hand. Thus, the spectacles are unieldy to carry.